A zero fret is typically a fret-like device placed at the headstock end of the neck of a stringed instrument, such as, without limitation, a banjo, guitar, mandolin, or bass guitar. A function of the zero fret is that it holds the strings a desired distance above the other frets on the instrument's fret board. Typical zero frets are either static and, therefore, can't be adjusted to selectively modify the tonal quality of the instrument or overly complex in their construction and use.
An adjustable zero fret that is effective in modifying tonal quality and easy to use is desired.